The dopamine transporter (DAT) has been identified as the cocaine receptor most linked with psychostimulant reward and reinforcement in the brain. Cloning DAT CDNAS from rat and man by Addiction Research Center molecular neurobiologists in previous Fys has allowed testing of the roles of discrete residues in the recognition of dopamine, cocaine and their analogs using site-directed mutagenesis. These approaches were especially explored in order to seek transporter regions selectively involved in cocaine binding and not in dopamine transport, a potential aid in development of anti-cocaine therapeutics. Elucidation of regions selectively involved in neurotoxin uptake but less implicated in dopamine uptake could yield sites for potential selective neurotoxin blockers. Analyses of over 30 dopamine transporter mutants, most prepared and analyzed over the last FY, has continued to yield interesting results. Replacement of a tyrosine located in transmembrane domain 4 yielded enhanced Km for dopamine uptake and substantially reduced affinity for cocaine analog, for example. Molecular modeling of the transporter has facilitated identification of targets for mutagenesis, and has provided useful scenarios for cocaine-transporter interactions. Analyses of mutants in several transmembrane regions and in extracellular domains documents several molecular regions at which cocaine and dopamine recognition sites can be separated.